1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly to a method of fabricating a color filter substrate for a liquid crystal display device.
2. Discussion of the Related Art
With the rapid development in information technology, flat panel display (FPD) devices having thin thickness, light weight, and lower power consumption have been introduced and developed.
Among these devices, liquid crystal display (LCD) devices are most widely used for monitors of notebook computers, monitors of personal computers and televisions due to high definition, high qualities, excellent moving images and high contrast ratio.
An LCD device includes two substrates and a liquid crystal layer interposed between the two substrates. Electrodes are formed on respective substrates, and the substrates are disposed such that the electrodes face each other. An electric field is induced between the electrodes when voltages are applied to the electrodes. The alignment direction of the liquid crystal molecules is controlled by varying the intensity of the electric field, and the transmittance of light through the liquid crystal layer is changed to display images.
FIG. 1 is an exploded perspective view of an LCD device according to the related art. As shown in FIG. 1, the LCD device includes an array substrate 10, a color filter substrate 20 and a liquid crystal layer 30. The array substrate 10 and color filter substrate 20 face each other, and the liquid crystal layer 30 is interposed therebetween.
The array substrate 10 includes gate lines 14 and data lines 16 on an inner surface of a transparent substrate 12. The gate lines 14 and the data lines 16 cross each other such that regions formed between the gate and data lines 14 and 16 are defined as pixel regions P. A thin film transistor Tr is formed at each crossing portion of the gate and data lines 14 and 16, and a pixel electrode 18 is formed in each pixel region P and connected to the thin film transistor Tr.
The color filter substrate 20 includes a black matrix 25, a color filter layer 26, and a common electrode 28 on an inner surface of a transparent substrate 22 facing the array substrate 10. The black matrix 25 has a lattice shape to cover a non-display region such as the gate lines 14, the data lines 16, the thin film transistors Tr, and so on. The color filter layer 26 includes red, green and blue color filter patterns 26a, 26b, and 26c repeatedly arranged in order. Each of the color filter patterns 26a, 26b, and 26c corresponds to each pixel region P. The common electrode 28 is formed on the black matrix 25 and the color filter layers 26 and over an entire surface of the substrate 22.
A sealant (not shown) is formed along peripheries of the array substrate 10 and the color filter substrate 20 to prevent liquid crystal molecules of the liquid crystal layer 30 from leaking. An alignment layer (not shown) is formed between the liquid crystal layer 30 and each of the array substrate 10 and the color filter substrate 20 to determine an initial direction of the liquid crystal molecules. A polarizer (not shown) is disposed on an outer surface of at least one of the array substrate 10 and the color filter substrate 20. A backlight unit (not shown) is disposed on an outer surface of the array substrate 10 to provide lights.
Scan signals for turning on/off the thin film transistors Tr are sequentially applied to the gate lines 14, and data signals are applied to the pixel electrodes 18 in the selected pixel regions P through the data lines 16. An electric field perpendicular to the substrates 12 and 22 is induced between the pixel electrodes 18 and the common electrode 28. The arrangement of the liquid crystal molecules is controlled by the electric field, and the transmittance of light is changed by varying the arrangement of the liquid crystal molecules to thereby display images.
In the LCD device, the color filter layer 26 is formed by a pigment dispersion method, a dyeing method, an electro-deposition method or a thermal imaging method. In general, the pigment dispersion method is more commonly used because it forms a fine pattern with good reproducibility.
FIGS. 2A to 2D are cross-sectional views showing a color filter substrate for a liquid crystal display (LCD) device in steps of a method of fabricating the same according to the related art. Here, the pigment dispersion method is used.
In FIG. 2A, a metallic material is deposited on or resin is applied to an entire surface of a transparent insulating substrate 60 and then patterned through a mask process to thereby form a black matrix 63, which has an opening op corresponding to each pixel region P. The black matrix 63 is disposed in a border between adjacent pixel regions P and surrounds each pixel region P. The black matrix 63 blocks light leakage, which is caused by irregular operation of liquid crystal molecules, in regions excluding pixel electrodes of an array substrate (not shown).
Here, the black matrix 63 has a thickness of 0.9 micrometers to 1.1 micrometers. If the thickness of the black matrix 63 is less than 0.9 micrometers, the black matrix 63 has a low optical density (OD) and transmits light. Accordingly, image qualities are lowered. On the other hand, if the thickness of the black matrix 63 is more than 1.1 micrometers, a step difference between the substrate 60 and the black matrix 63 is considerably high. This causes disconnection of resist layers for color filter patterns to be formed in following steps.
In FIG. 2B, a color resist, which may be one of red, green and blue resists, for example, a red one, is applied to an entire surface of the substrate 60 including the black matrix 63 thereon by a spin coating or bar coating method to thereby form a red resist layer 66. A mask 90 having a light-transmitting portion TA and a light-blocking portion BA is disposed over the red resist layer 66. The red resist layer 66 is exposed to light through the mask 60. Here, the red resist layer 66 is shown to have a negative property. That is, a portion of the red resist layer 66 that is not exposed to light is removed after a developing process.
In FIG. 2C, the light-exposed red resist layer 66 of FIG. 2B is developed, and a red color filter pattern 67a is formed in a first pixel region P1 among the pixel regions P. The red color filter pattern 67a overlaps the black matrix 63 surrounding the first pixel region P1.
In FIG. 2D, green and blue color filter patterns 67b and 67c are respectively formed in second and third pixel regions P2 and P3 on the substrate 60 through similar processes to the red color filter pattern 67a in the first pixel region P1. The green and blue color filter patterns 67b and 67c overlap the black matrix 63.
Then, an overcoat layer (not shown) is formed on an entire surface of the substrate 60 including the red, green and blue color filter patterns 67a, 67b and 67c by applying an organic insulating material to the red, green and blue color filter patterns 67a, 67b and 67c. The overcoat layer protects the red, green and blue color filter patterns 67a, 67b and 67c and flattens the surface of the substrate 60 having the red, green and blue color filter patterns 67a, 67b and 67c. Next, a transparent conductive material such as indium-tin-oxide or indium-zinc-oxide is deposited on the overcoat layer to thereby form a common electrode (not shown). Accordingly, the color filter substrate for an LCD device is completed. Here, the common electrode may be omitted in a color filter substrate for an in-plane switching (IPS) LCD device.
However, in the pigment dispersion method, three patterning processes are performed, each of which includes steps of applying a color resist, exposing the color resist through a mask and developing the color resist. Accordingly, a production line is long and complicated. In addition, manufacturing time and costs are increased, and productivity is lowered.